The westbound Union Pacific train, with three locomotives and 75 cars, hit the middle of the southeast-bound BNSF train, which had two locomotives and 60 cars, Sumwalt said. The collision occurred where the railroads’ tracks intersected, authorities said. The BNSF train was carrying scrap metal; the Union Pacific’s load was not disclosed.

Each train was staffed by an engineer and conductor.

The collision derailed two locomotives and 11 cars from the Union Pacific train and 13 cars from the BNSF train, Sumwalt said.

Bridge Hit Before

Spans 2 and 3 of the five-span bridge collapsed after the No. 3 column was struck by one of the railcars, which was “wrapped around” the support, Sumwalt said.

The collision derailed a total of 24 cars and two locomotives from the two freight trains at an intersection.

Sumwalt said the 367-foot-long bridge, owned by the Missouri Department of Transportation, was last inspected Feb. 25 and rated a 7 on a scale of 1 to 9, which classified its condition as “good.”

However, he added, the No. 3 column was also struck by another railcar in a derailment on Jan. 30 of this year. The column was inspected after that accident and found to have no structural damage, Sumwalt said.

This time, Sumwalt said, BNSF personnel did not even realize the train had been in a collision until after the emergency braking system engaged and the conductor got out to walk the track to investigate.

The conductor, who had more than 10 years of experience, discovered the collision about a dozen cars back, Sumwalt said.

Replacing the bridge will cost about $3 million, said Mark Shelton, engineer for MODOT's southeast region.

“The damage is very extensive,” Shelton told STLtoday.com. “We’re going to end up removing the entire bridge and completely replacing it.”

Investigation Focus

NTSB investigators were expected to remain on the scene for up to a week. The trains’ track image recorders and event data recorders were flown back to NTSB’s lab in Washington on Saturday for examination.

Image recorders were mounted on the front of each train and on at least one rearward-facing locomotive, Sumwalt said.

The derailment took out two spans of a highway overpass that was being traveled by two cars. The derailment, bridge collapse and ensuring fire injured seven people. Their conditions were not available.